A typical system for natural gas includes a large network of interconnected, sealed conduit (i.e., pipeline) and a series of pressure reducers for conveying the gas from a storage facility or source, usually under a relatively high pressure, to individual customers, usually at lower pressure. Throughout a large commercial natural gas pipeline system there may be a number of different operating pressure ranges for the gas according to the overall design of the system. By way of example, the system could include a storage field system, which operates at very high pressure (in the range of 500-1,000 PSI), or a transmission system, which operates over longer distances and might have a high pressure (in the range of 150-500 PSI or at 7" W.C.) or a customer-owned system which operates at low pressure (7" W.C.).
The present invention is intended to be used in all types of systems and at all pressures from low to very high, as described above. And as used herein, the term "natural gas pipeline system" is intended to include all such factions of a system, from storage field or source through transmission lines, distribution lines and low-pressure applications.
Obviously, faults or leaks may occur in any portion of a natural gas pipeline system, and it is highly desirable, when utility maintenance teams are working on a given fault, to monitor the gas pressure. Normally, the gas pressure is monitored downstream of the work area because it is desired to maintain service while repairs are being made. The fault area is usually isolated from the rest of the system; and a by-pass or shunt is employed to route the gas around the fault after the fault area is isolated. This enables the system to continue to transmit or distribute the gas while the fault is being corrected. It is thus important that maintenance crews be alerted to high pressure (for safety reasons) as well as low pressure (to maintain service).
There are a number of shortcomings with existing, commercial pressure monitors. Primarily, the most common portable pressure monitors have a display which presents, in visual form, a reading representative of the pressure, in pounds per square inch (PSI) or inches of water column (W.C.), of the gas being monitored. These instruments are sufficiently accurate to be useful, but they require constant or repeated monitoring at short intervals to detect variances from a desired range. This distracts from the work crew's primary objective-namely, to repair the fault. Moreover, little or no warning is provided in the case of a pressure surge when these instruments are not being immediately attended by a workman. Further, if the monitor simply displays a reading, the operator must be constantly aware of the safe limits for the particular section of the network in which the work area is located. The possibility for human error is thus present even if the readings are accurate and regularly monitored.